Torque value on sprocket nuts?

[1fastmofo]

Anyone know what to torque the nuts to that hold the rear sprocket? This is for a Honda F2... (91')

Thanks,
Ray

[1fastmofo]

I found it...

90 Newton Meters or
65 lb-ft

[Super Dave]

The torque values are established for street bikes;  stuff that will probably not be touched again for 15,000 miles.  If you're gonna follow some of those values, you might want to replace some of the fasteners over time...they will become fatigued from stretching under torque.

[tzracer]

The torque value chosen for a fastener is based upon the load needed and the fastener size and grade, not whether it is for a street bike or a race bike. For safety, a street bike usually has a larger fastener than needed (hence requiring a higher torque value).

A bolt is like a spring. When you tighten a bolt it stretches. The load that is the result of stretching of the bolt is what does the holding. The load from the bolts causes friction between the sprocket and the sprocket carrier. This friction is what keeps the sprocket in place (not the bolts themselves - the bolt should have no shear load). The torque is chosen to give enough load to keep the sprocket from moving. If the bolts are not tight enough, the sprocket can move and press on the bolts, this can cause the bolts to break. Under tightening is just as bad as over tightening.

As long as you do not tighten a bolt past its yield point, it can be reused many times. After a bolt is removed it will return to its original length as long as you have not taken it past its yield point. The wear on the threads and underside of the head and nut will cause it to be replaced before any problem from repeated use. When I worked at Buell, Erik chose fasteners so that they gave the proper load at 75% of yield (this is quite common).

In the building of a bike, the needed load will be calculated or experimentally determined. A safety factor of about 20% will be added (a race bike may use a smaller amount). Then the bolt will be chosen. On street bikes, bolts larger than necessary are often chosen. To tighten to 75% yield, a larger bolt or higher grade bolt requires more torque. Hence the torque value looks high, but this is due to the size of the bolt chosen. ISTR my RC51 using 12mm bolts for the rear sprocket.

Torque to the book spec (you do own the service manual?). Any time you remove the sprocket, inspect the threads, when they start to wear (looks like the threads are being pulled to one side), replace all the bolts and nuts.